The menstrual cycle is regulated by fluctuating sex hormones from the pituitary gland. It consists of four phases: the follicular phase where follicles in the ovaries mature and estrogen levels rise, ovulation where a mature egg is released, the luteal phase where the corpus luteum produces progesterone, and menstruation where the uterine lining sheds if pregnancy does not occur. The cycle typically lasts around 28 days and involves changes in the ovaries and uterus governed by hormones that prepare the body for potential pregnancy each month.